Ever since the invention of the incandescent lamp in 1879 and the direct current charging system, ca. 1900, such lamps have been used in motor vehicles for signalling. Later automatic flasher switches were invented and applied in turn signalling systems. One such flasher is documented in U.S. Pat. No. 3,218,415. Flasher switches are hereinafter referred to as "flashers".
A typical automotive exterior signalling system of the prior art comprises a battery for direct current (d.c.) electricity having a positive terminal and a connection to system ground, a steering column mounted turn signal switch having left detent, Off, and Right detent positions, front and rear, left and right signalling lamps, a signal flasher which causes the blinking of the turn signalling lamps, and a turn signal switch cancelling mechanism.
A flasher of the prior art is a two terminal thermoelectrical device, which, when connected in series with parallel connected incandescent lamps, will cause the lamps to flash periodically when d.c. is forced through the circuit.
When an operator of said system wants to signal a turn, he moves the turn signal switch to the appropriate detent position. The turn signal switch routes current from the battery through the flasher, and on through the lamps to system ground. For the first 3/4 second (s.) or so after said switching, the lamps are lit (a MARK); thereafter they will be unlit (a SPACE) and lit periodically with a period of approx. 0.8 s., MARK and SPACE lasting 0.4 s. each, until the turn signal switch is moved back to the Off position, at which time the lamps are immediately extinguished.
The commonly used thermoelectric flasher of the prior art has proven adequate but has one shortcoming: If an operator forgets to turn Off the turn signal switch in a situation where the cancelling mechanism does not do it, the turn signal lamps flash indefinitely.
The present invention is an electronic version of the flasher. It has the additional feature of automatically terminating a flashing sequence, if the turn signal switch is left in a detent position for more than a certain fixed interval. This feature is called the "timeout" feature herein; said interval is called the "timeout interval".
Turn signalling systems having the timeout feature have been used for some time on motorcycles, necessary because there is no cancelling switch. Yet, the timeout feature has not been worked into automotive systems, the closest thing so far being an audible alarm which sounds after approx. 40 s. e.g., a 1989 Oldsmobile. This particular scheme has the drawbacks that there are several other sources of alarms, and the alarm has to be very loud to overcome road noise.
The application of motorcycle timeout circuitry to automobiles is not straight forward, because: (a) The turn signal switch on a car differs from that of a motorcycle. (b) It is desirable to retain the mechanical cancelling mechanism in the automotive system, but motorcycles don't have this, and (c) In an automotive system, with each MARK there is a current surge of approx. 30 A. (Amperes) through two standard turn signal lamps wired in parallel. A flasher switch can tolerate this, but a junction transistor which can tolerate this is expensive.
Nonetheless, transistorized flashers have been used, one such being on Ford trucks (except F100), wherein the flasher doubled as a hazard warning flasher. (See 1970 truck shop manual, loc cit).
Electronic flashers of the prior art have accommodated some but not all of the above factors. U.S. Pat. No. 4,254,397 seems not to have addressed the third of these, and it produces a long initial MARK. The circuits of U.S. Pat. Nos. 4,290,048, 4,302,748, and 4,792,785 are intended especially for motorcycles. The first of these employs a relay; the second has three oscillators; the third is intended solely for motorcycles and employs a handlebar angle turning sensor and a traversed-distance transducer.
Two further considerations are cost and size. The common flasher of the prior art costs approx. three dollars, a cost which would be hard to beat with any of the electronic flashers of the prior art, especially those employing junction transistors as the main switching element, such as in U.S. Pat. Nos. 4,254,397, 4,290,048, 4,302,748, 4,792,785, UK 2,104,738A, and UK 2,084,413A. Regarding size, relays and capacitors are components which must be discrete and add considerably to size. Of the above referenced documents, capacitor counts are six, two, six, twelve, four, three, and six, respectively. Relays are specified in U.S. Pat. No. 4,290,048 and Ger. 28 27 212. A magnetically actuated turn signal switch return mechanism is part of the signalling system of U.S. Pat. No. 4,792,785, as part of the prior art with respect to that invention.